Keying circuit employing thermionic valves



March 7, 1950 P. .1. NEILSON 2,499,604

KEYING CIRCUIT EMPLOYING THERMIONIC VALVES Filed April 18, 1947 our/=10? 9/ I -7ot/ I our/ 07' i INVENTOR PMs 54s JT Ai/zsoxv BY k w ATTORN EY Patented Mar. 7, 1950 KEYING CIRCUIT EMPLOYING THERMIONI VALVES I Phineas Jack Neilson, Chelmsford, England, assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporae tion of Delaware Application April 18, 1947, Serial No. 742,445 In Great Britainseptember 27, 1945 Section 1, Public Law 690, August 8, 1946 Patent expires September 27, 1965 8 Claims.

This invention relates to keying circuits employing thermionic valves, particularly to such circuits for the on-and-ofiE-keying of alternating electrical currents or potentials, such as tone-frequency currents or potentials.

It is well known, that unless steps are taken, the keying of alternating currents or potentials in circuits using thermionic valves is accompanied by transients or so-called key-clicks. In order to suppress these transients or key-clicks, it has been usual, heretofore, to employ valves connected in push-pull, advantage being taken of the anti-phasal relationships of the potentials at the output electrodes of the two valves or systems of valves employed.

In carrying out the present invention, advantage is taken of the anti-phasal relationship of the potentials at the anode and one grid of a multi-grid valve under appropriate conditions of bias on another grid of the valve.

Hereinafter, though reference will, for convenience of diction, be made to tone currents or potentials, I do not Wish to be too rigidly limited to the currents or potentials thus indicated, for clearly currents or potentials having a frequency outside the audible range are possible.

According to this invention, a valve keying circuit includes a multi-grid valve to one grid of which, in operation, a tone potential is applied so as to produce anti-phasal tone potentials on two other electrodes and to another grid of which a keying bias potential is applied to cut oil in the keying rhythm the electron stream in said valve, and an output circuit having its two input terminals connected respectively to said two other electrodes.

The output circuit may include a transformer having a centre tapped primary Winding and a secondary winding, a connection from a point on one side of the centre tap of said primary-winding to one of said two other electrodes and a connection from a point on the other side of said centre top to the other of said two other electrodes. v

Alternatively, the output circuit may includ two separate series connected impedances, the point of juncture of the two impedances serving for the supply of direct positive potential and the outer ends of the separate impedances being connected one end to one and the other end to .the essential elements of a different embodiment of my invention.

Valve V, which may be assumed to be an EF50, or the type known in the United States as a 6AC7, has its cathode e connected through resistors RI, R2 and R3, to the earthed negative terminal of a source E (not shown) of anode current, its first grid gl connected through a resistor R4 to the negative terminal of a source C (not shown) of bias potential, the positive terminal of which is connected to the earthed base line, its second grid 2 connected to one end of the primary winding p of transformer T, its third grid 93 connected to one terminal of a source of tone potential (not shown) whose other terminal is connected to the earthed base line, and its anode a connected to the other terminal of primary winding p of transformer T. The mid-point of the primary winding p is connected to the positive terminal of said source of anode current. A key K has one terminal connected to grid 9! of the valve and the other terminal connected to a suitable point on the resistor network RI R2, R3.

The pentode V has its bias conditions such that screen grid or electron-receiving electrode g2 and janode or electron-receiving electrode a currents are equal and of opposite phase for signals impressed on the suppressor grid or control electrode gl. The anode and screen grid circuits are completed by being connected to the positive terminal of the source E, .thene'gative terminal of which is grounded as described above and is also connected tocathode .ethr'oughresistors RI, R2, and R3. Control electrode or first grid gl is biased negatively with respect to cathode e from a source C when key K is open,,this negativebias being reduced or decreasedby closure of key Kto connect 2,499,604 5 6 8. A keying circuit, comprising a tube having a pear, and means for varying the potential on said control grid, an electron-receiving grid, an anode control grid in accordance with keying operations.

and an auxiliary grid, means for applying a volt- PHINEAS JACK NEILSON. age to be keyed to said auxiliary grid, means for applying direct potentials to the electrodes of said 5 REFERENCES CHED tube to produce antimhawl Voltages on Said The following references are of record in the anode and said electron-receiving grid in response file of this patent to the application of said voltage to said auxiliary grid, when said tube is conductive, an output im- UNITED STATES PATENTS pedance between said anode and said electron-re- 10 Number Name Date ceiving grid wherein said anti-phasal voltages ap- 2,339,879 Tunick NOV 27, 1945 

